The amount of oxygen in the air at high altitudes is much less than at sea
level. As a result, oxygen deprivation, or hypoxia, is one of the greatest
threats high altitude climbers face. Students can determine the concentration of
oxygen in air at their location in this activity. Divide the class into teams and distribute
the materials and activity
sheet.

Start by asking students to predict how much of the air is oxygen. Then
have them determine the volume of oxygen in air within a test tube by removing
the oxygen through the oxidation of steel wool (plain steel wool is available
at most hardware stores). Make sure that students understand that as the steel
wool rusts, it is using oxygen.

Familiarize yourself with the formula you will use with students to calculate
the amount of oxygen with Calculating the Percentage of Oxygen in the Air in
Activity Answer below. How do students' results compare with their predictions? Note that
air is about one-fifth oxygen. Have students explain why their results might
differ. Then have them estimate the amount of oxygen they think is at the
summit of Mt. Everest and defend their reasoning.

Conclude with a discussion
of the difference in oxygen levels and reasons why.

Prior to the activity, students should understand that as steel wool rusts, it
is using oxygen. Another term for rusting is oxidation. As steel wool undergoes
oxidation, the iron molecules in the steel wool combine with oxygen in the air
to form a new compound, iron oxide, or rust.

The steel wool should be wet or it will not rust. As the steel wool begins to
rust inside the test tube, the water level in the tube rises to displace the
oxygen used in the oxidation process. The water is pushed up by the air above
the surface of the water in the beaker. The steel wool stops rusting when there
is no more oxygen available in the air sample, or when the steel wool is
completely used up. Students should observe that the rusting process stops at
the same time that the water level stops changing. As a control, the water
level in the test tube without steel wool should remain approximately the same.
The rusting process will usually stop after one day, but students can observe
over several days to confirm that the water level is no longer changing.

Oxygen makes up about one-fifth, or approximately 21 percent, of air. While the percentage of oxygen
in the air remains the same at sea level and on the summit of Mt. Everest, oxygen is less
concentrated at high altitudes because of the pressure differential, thus making it more
difficult for climbers to get the amount of oxygen they need.

Most climbers who attempt to summit Everest bring supplemental
oxygen with them to aid their breathing. Lack of oxygen can cause many stresses
to the body, including obvious symptoms like gasping for breath, as well as
more subtle symptoms like lack of ability to retain body temperature, loss of
appetite, difficulty making decisions and thinking clearly, and fatigue.

Calculating the Percentage of Oxygen in the Air
To find the volume of oxygen in the test tube with the steel wool, have students compare
the original volume of air to the final volume of air. To find the original volume of air,
have them fill the test tube to the first mark with water and measure the volume in a graduated
cylinder. To find the final volume of air, have students fill the test tube to the final mark
and measure. Subtract the final volume from the original volume to find the volume of oxygen.
Divide this number by the original volume and multiply that ratio by 100 to get the percent of
oxygen in the air.